In computer networks a plurality of nodes are connected by a plurality of links. Often the connection of links and nodes is not orderly, symmetrical or follows an established pattern. Also there is often a plurality of possible routing paths between a first and second node. Methods are known to determine a plurality of routing paths in such disorganized networks. When a plurality of routing paths are available, one path needs to be selected for the actual data transmission. The choice of the actual path is often based on characteristics of the different paths. Metric values are used to represent the characteristics of a path, and each path often contains a plurality of different links and nodes which have different metric values for the characteristics that are important in selecting a routing path. A metric value is determined for each characteristic of each path by combining the metric values of each link and node in the path. This metric combining in this document will be referred to as "metrically adding". However depending on the characteristic, the combining of metric values is not always by simple mathematical addition. When the characteristic is time delay or distance, the time delay or distance for each link and node is simply added. When the characteristic is a data rate type characteristic, the metric value for the path is the lowest data rate of the links and nodes. When a characteristic is similar to a standard deviation of noise, the standard deviation of noise for a routing path is a more complicated combination or addition of the standard noise deviations of the individual links and nodes.
When the number of nodes and links in a computer network is relatively small, each node can store the metric values for all the links and nodes in the network. When a node wishes to communicate with another node, a plurality of routing paths are determined and the node calculates the metric values for the different characteristics of each routing path by metrically adding the metric values for the individual characteristics of each link and node in the path. When the number of links and nodes in a computer network is relatively large, it becomes impossible, or at least impractical, for a node to store all the metric values of all the links and nodes in the network. Instead of limiting the size of the network, it has been proposed to layer the network in a hierarchical manner.
In a layered network, a group of nodes and the links connecting those nodes are formed into a peer group. A computer network can then have a plurality of peer groups. Each node in a peer group contains actual information for the links and nodes in its own peer group. The node only contains summary information for other peer groups to which it does not belong. In this way, each node does not need to store large amounts of routing information and simplifies the routing process.
For the hierarchical layering of computer networks to operate properly, the summarization of the routing information for other peer group's must reasonably reflect the routing properties of the peer group being summarized, while substantially reducing the amount of information needed to describe that peer group. Typically summarization methods have been "and-hoc" or "heuristic" in nature.